1. Field of the Invention
The present invention relates to a centralized supervisory control system for centrally supervising a plurality of supervised apparatuses.
2. Description of the Prior Art
Centralized supervisory control systems are required accurately to report events or irregularities occurring in any of a plurality of apparatuses under their control, along with time-of-day indications corresponding to such occurrences. What is required for such a control system involves notifying personnel at a centralized control center of information about failures and other events occurring in any of a plurality of supervised apparatuses under system control, the personnel being also informed of the times of day corresponding to such occurrences.
A typical prior art centralized supervisory control system will be described with reference to FIG. 1. In the centralized supervisory control system of FIG. 1, a centralized supervisory control center 2 is connected to a plurality of stations 1a, 1b and 1c. Each of the stations 1a, 1b and 1c comprises an intermediate control apparatus 3 and a plurality of supervised apparatuses 4 through 8 connected to the apparatus 3. The intermediate control apparatus 3 continuously collects information about the supervised apparatuses 4 through 8 and forwards the collected information to the centralized supervisory control center 2.
On receiving the information about a failure in any supervised apparatus from the intermediate control apparatus 3, the centralized supervisory control center 2 attaches a time-of-day indication to that information. The received information is displayed on a monitor or the like together with the corresponding time-of-day indication. By observing the displayed contents, the operator at the center 2 checks the status of the supervised apparatuses 4 through 8 in each of the stations 1a, 1b and 1c.
If the centralized supervisory control center 2 is stopped for maintenance or other purposes or if any of the lines connected to the centralized supervisory control center 2 is disconnected, the time-of-day indication of the information received during service disruption is made the same as that given when the centralized supervisory control center is back in service. This is because only when information is received is the time-of-day indication attached thereto made available for display. As a result, the centralized supervisory control center 2 is barred from finding the exact time of day at which a failure occurred in any of its subordinate apparatuses.
Where the scale of the centralized supervisory control system is expanded, it takes time to collect information about the supervised apparatuses under control of the system. This also results in the inability of the system to detect the exact times of failures in its subordinate apparatuses. In addition, where a display device is connected to the intermediate control apparatus, the time-of-day indication attached to a certain event by the intermediate control apparatus may differ from that attached thereto by the centralized supervisory control center.